cedriver:This is during the backswing that it shrinks up.
This is common to all clubs except putter AFAIK. Measurement of initial shrinking of the light blue area around the ding, from idle to 100% meter, on my screen:
Driver: 4 => 2 cm
(continuously widening towards shorter clubs)
8i 4.5 => 2.5 cm
(...)
64° 5 => 3 cm
Putter 8.7 => 8.5 cm
You'll notice forgiveness if you miss the ding and shoot straight regardless. The relevant characteristics when hitting the ding is precision.